Hi Tilman,
also thanks from my side for your answer.
However, the question was exactly what Jacques asks: How can I mix at the node level transient and persistent data ("rows"), not how one can mix transient and persistent attributes at one node.
I guess that should be possible implementing my own data access classes and use a transient attribute to distinguish transient and persistent records.
I'm asking if someone did that before or is there an easier way to achieve that?